磷酸二酯酶抑制剂与呼吸道疾病

磷酸二酯酶(PDE)存在于许多炎症细胞及结构细胞中,目前已发现11种.PDE抑制剂主要抑制体内环磷酸腺苷(cAMP)及环磷酸鸟苷(cGMP)水解,使细胞内cAMP及cGMP浓度增加,引起一系列生理功能,如平滑肌舒张、减轻细胞炎症及免疫反应等.PDE4特异性水解cAMP,选择性PDE4抑制剂具有广泛抗炎作用,如抑制细胞趋化,抑制中性粒细胞、嗜酸粒细胞、巨噬细胞及T细胞细胞因子及化学趋化物质释放.第二代PDE4抑制剂Cilomilast和Roflumilast已进入临床实验阶段,并已证实对支气管哮喘(简称哮喘)及慢性阻塞性肺疾病(chronic obstructive pulmonary disease,COPD)有效.由于胃肠道副作用,这类药物临床应用受到一定限制.PDE5可特异性水解cGMP,对缺氧性肺动脉高压和血管重塑有效.PDE3和PDE7特异性水解cAMP,PDE7参与T细胞激活.目前其他PDE抑制剂与PDE4抑制剂混合制剂正在研发中.PDE4-PDE7双重抑制剂可能对哮喘及COPD更有效.PDE3-PDE4双重抑制剂具有更强的支气管舒张作用及气道保护作用.     

Treating COPD with PDE 4 inhibitors

While the pathogenesis of chronic obstructive pulmonary disease (COPD) is incompletely understood, chronic inflammation is a major factor. In fact, the inflammatory response is abnormal, with CD8⁺ T-cells, CD68⁺ macrophages, and neutrophils predominating in the conducting airways, lung parenchyma, and pulmonary vasculature. Elevated levels of the second messenger cAMP can inhibit some inflammatory processes. Theophylline has long been used in treating asthma; it causes bronchodilation by inhibiting cyclic nucleotide phosphodiesterase (PDE), which inactivates cAMP. By inhibiting PDE, theophylline increases cAMP, inhibiting inflammation and relaxing airway smooth muscle. Rather than one PDE, there are now known to be more than 50, with differing activities, substrate preferences, and tissue distributions. Thus, the possibility exists of selectively inhibiting only the enzyme(s) in the tissue(s) of interest. PDE 4 is the primary cAMP-hydrolyzing enzyme in inflammatory and immune cells (macrophages, eosinophils, neutrophils). Inhibiting PDE 4 in these cells leads to increased cAMP levels, down-regulating the inflammatory response. Because PDE 4 is also expressed in airway smooth muscle and, in vitro, PDE 4 inhibitors relax lung smooth muscle, selective PDE 4 inhibitors are being developed for treating COPD. Clinical studies have been conducted with PDE 4 inhibitors; this review concerns those reported to date.     

Stem cell factor induces eosinophil activation and degranulation: mediator release and gene array analysis

Eosinophils are effector cells that play an important role in the damage induced by the allergic process by releasing inflammatory mediators and proteolytic factors after activation. Stem cell factor (SCF) is a primary cytokine involved in hematopoiesis and mast cell differentiation, proliferation, and activation. Studies have also indicated that SCF is directly involved in pathogenesis of allergic airway inflammation. In the present study, we examined the ability of SCF to activate murine eosinophils for increased mediator release and up-regulation of chemokines. Initial data demonstrated that eosinophils have significant levels of surface c-kit protein, SCF receptor. SCF-activated eosinophils degranulate and release eosinophil peroxidase and leukotriene C(4) in a dose-dependent manner. In addition, SCF was further shown to induce the release of CC chemokines, RANTES, macrophage-derived chemokine (MDC), macrophage inflammatory protein-1beta (MIP-1beta), and C10 from eosinophils. To identify the extent of SCF-induced activation of eosinophils, we also performed gene array analysis using an array containing 1153 genes related to inflammation, including cytokines and their receptors, growth factors, structural and cytoskeletal genes, signal transduction genes as well as several other classes related to immune/inflammatory responses. The gene analysis indicated that more than 150 genes were significantly up-regulated in eosinophils after SCF stimulation. The gene array results were verified using a quantitative real-time polymerase chain reaction analysis to identify the expression of several chemokine and chemokine receptor genes. Altogether, these studies indicate that SCF is a potent eosinophil degranulator and activator that may play a number of roles during an inflammatory/immune response.     

The role of chemokines in rheumatoid arthritis and osteoarthritis

The directed movement of immune cells is highly dependent on the chemokine network. Chemokines are key molecules early in the embryogenesis of lymph nodes and throughout adult life, where they regulate immune responses against pathogens. Although immune cells are best known for expressing chemokine receptors, through which they can respond to matching chemokines, endothelial cells also express chemokine receptors. The directed movement of endothelial cells facilitates angiogenesis. In chronic inflammatory conditions, such as rheumatoid arthritis (RA), chemokines are abundantly present at the site of inflammation and form a group of potential therapeutic targets. Some agents that block chemokine-chemokine receptor interaction are already under clinical investigation. The expression of chemokine receptors has also been found in cell types other than immune cells and endothelial cells. Chondrocytes, for instance, express several chemokine receptors. Elucidating their function may provide new insights into joint degradation in RA as well as in other conditions, including osteoarthritis (OA).     

HIV-1-suppressive factors are secreted by CD4+ T cells during primary immune responses

CD4+ T cells are required for immunity against many viral infections, including HIV-1 where a positive correlation has been observed between strong recall responses and low HIV-1 viral loads. Some HIV-1-specific CD4+ T cells are preferentially infected with HIV-1, whereas others escape infection by unknown mechanisms. One possibility is that some CD4+ T cells are protected from infection by the secretion of soluble HIV-suppressive factors, although it is not known whether these factors are produced during primary antigen-specific responses. Here, we show that soluble suppressive factors are produced against CXCR4 and CCR5 isolates of HIV-1 during the primary immune response of human CD4+ T cells. This activity requires antigenic stimulation of na?ve CD4+ T cells. One anti-CXCR4 factor is macrophage-derived chemokine (chemokine ligand 22, CCL22), and anti-CCR5 factors include macrophage inflammatory protein-1 alpha (CCL3), macrophage inflammatory protein-1 beta (CCL4), and RANTES (regulated upon activation of normal T cells expressed and secreted) (CCL5). Intracellular staining confirms that CD3+CD4+ T cells are the source of the prototype HIV-1-inhibiting chemokines CCL22 and CCL4. These results show that CD4+ T cells secrete an evolving HIV-1-suppressive activity during the primary immune response and that this activity is comprised primarily of CC chemokines. The data also suggest that production of such factors should be considered in the design of vaccines against HIV-1 and as a mechanism whereby the host can control infections with this virus.     

Dendritic cells exposed to extracellular adenosine triphosphate acquire the migratory properties of mature cells and show a reduced capacity to attract type 1 T lymphocytes

We previously reported that chronic stimulation with low, noncytotoxic doses of extracellular adenosine triphosphate (ATP) induced a distorted maturation of dendritic cells (DCs) and impaired their capacity to initiate T-helper (Th) 1 responses in vitro. Here, we examined the effects of ATP on chemokine-receptor expression and chemokine production by DCs. ATP strongly induced expression of CXC chemokine receptor 4 on both immature and lipopolysaccharide (LPS)-stimulated DCs and slightly up-regulated CC chemokine receptor (CCR) 7 on both DC types. In contrast, ATP reduced CCR5 expression on immature DCs. These effects were confirmed at both the messenger RNA and protein levels and were not produced by uridine triphosphate (UTP). Consistent with the changed receptor expression, ATP increased migration and intracellular calcium of immature and mature DCs to stromal-derived factor 1 (CXC ligand [CXCL] 12) and macrophage inflammatory protein [MIP] 3 beta (CC ligand [CCL] 19), whereas responses to MIP-1 beta (CCL4) were reduced. DCs are an important source of chemokines influencing recruitment of distinct T-lymphocyte subsets. ATP, but not UTP, significantly reduced LPS-induced production of interferon-inducible protein 10 (CXCL10) and regulated upon activation, normal T-cell expressed and secreted chemokine (CCL5); increased secretion of macrophage-derived chemokine (CCL22); and did not change production of thymus and activation-regulated chemokine (CCL17). Consistent with these findings, supernatants from ATP-treated mature DCs attracted Th1 and T-cytotoxic 1 cells less efficiently, whereas migration of Th2 and T cytotoxic 2 cells was not affected. Our data suggest that ATP provides a signal for enhanced lymph node localization of DCs but that it may, at the same time, diminish the capacity of DCs to amplify type 1 immune responses.     

Role of chemokines and their receptors in viral persistence and liver damage during chronic hepatitis C virus infection

Chemokines produced in the liver during hepatitis C virus（HCV） infection induce migration of activated T cells from the periphery to infected parenchyma.The milieu of chemokines secreted by infected hepatocytes is predominantly associated with the T-helper cell/Tc1 T cell（Th1/Tc1） response.These chemokines consist of CCL3（macrophage inflammatory protein-1α;MIP-1α）,CCL4（MIP-1β）,CCL5（regulated on activation normal T cell expressed and secreted;RANTES）,CXCL10（interferon-γ-inducible protein-10;IP-10）,CXCL11（interferon-inducible T-cell α chemoattractant;I-TAC）,and CXCL9（monokine induced by interferon γ;Mig） and they recruit T cells expressing either CCR5 or CXCR3 chemokine receptors.Intrahepatic and peripheral blood levels of these chemokines are increased during chronic hepatitis C.The interaction between chemokines and their receptors is essential in recruiting HCV-specific T cells to control the infection.When the adaptive immune response fails in this task,non-specific T cells without the capacity to control the infection are also recruited to the liver,and these are ultimately responsible for the persistent hepatic damage.The modulation of chemokine receptor expression and chemokine secretion could be a viral escape mechanism to avoid specific T cell migration to the liver during the early phase of infection,and to maintain liver viability during the chronic phase,by impairing non-specific T cell migration.Some chemokines and their receptors correlate with liver damage,and CXCL10（IP-10） and CXCR3 levels have shown a clinical utility as predictors of treatment response outcome.The regulation of chemokines and their receptors could be a future potential therapeutic target to decrease liver inflammation and to increase specific T cell migration to the infected liver.     

Cyclic nucleotide phosphodiesterase profiling reveals increased expression of phosphodiesterase 7B in chronic lymphocytic leukemia

Cyclic nucleotide phosphodiesterase (PDE) isoforms can influence disease pathogenesis and be novel therapeutic targets. Because lower cAMP levels may contribute to the decreased apoptosis that occurs in chronic lymphocytic leukemia (CLL), we assessed the expression levels of PDE isoforms in peripheral blood mononuclear cells (PBMC) of healthy adults and patients with CLL. We found a unique PDE mRNA signature in CLL: higher levels than in normal PBMC of PDE7B (increased ≈23-fold) and lower levels of PDE3B, 4D, 5A, and 9A mRNA (each decreased ≈30-fold). Increased PDE7B mRNA in CLL correlates with a 10-fold-higher expression of PDE7B protein and results in an increased contribution of PDE7 to total PDE activity. Consistent with the higher level of PDE7B expression, inhibitors of PDE7 (BRL-50481, IR-202) and a dual PDE4/PDE7 inhibitor (IR-284) selectively increase apoptosis in CLL cells compared with normal PBMC or B cells. Apoptosis of CLL cells promoted by inhibitors of PDE7 and PDE4/7 is attenuated by PKA inhibition, occurs via a mitochondrial-dependent process, and is associated with increased cAMP accumulation and down-regulation of the antiapoptotic protein survivin and of PDE7B. The increase in PDE7B expression and PDE7 inhibitor-promoted apoptosis implicates PDE7B as a drug target in CLL. Our findings identify a unique PDE signature in CLL and illustrate the utility of broad analyses of PDE isoform expression in human disease.     

Apoptosis inhibitor of macrophage (AIM) is required for obesity-associated recruitment of inflammatory macrophages into adipose tissue

Infiltration of inflammatory macrophages into adipose tissues with the progression of obesity triggers insulin resistance and obesity-related metabolic diseases. We recently reported that macrophage-derived apoptosis inhibitor of macrophage (AIM) protein is increased in blood in line with obesity progression and is incorporated into adipocytes, thereby inducing lipolysis in adipose tissue. Here we show that such a response is required for the recruitment of adipose tissue macrophages. In vitro, AIM-dependent lipolysis induced an efflux of palmitic and stearic acids from 3T3-L1 adipocytes, thereby stimulating chemokine production in adipocytes via activation of toll-like receptor 4 (TLR4). In vivo administration of recombinant AIM to TLR4-deficient (TLR4(-/-)) mice resulted in induction of lipolysis without chemokine production in adipose tissues. Consistently, mRNA levels for the chemokines that affect macrophages were far lower in AIM-deficient (AIM(-/-)) than in wild-type (AIM(+/+)) obese adipose tissue. This reduction in chemokine production resulted in a marked prevention of inflammatory macrophage infiltration into adipose tissue in obese AIM(-/-) mice, although these mice showed more advanced obesity than AIM(+/+) mice on a high-fat diet. Diminished macrophage infiltration resulted in decreased inflammation locally and systemically in obese AIM(-/-) mice, thereby protecting them from insulin resistance and glucose intolerance. These results indicate that the increase in blood AIM is a critical event for the initiation of macrophage recruitment into adipose tissue, which is followed by insulin resistance. Thus, AIM suppression might be therapeutically applicable for the prevention of obesity-related metabolic disorders.     

PDE1B2 regulates cGMP and a subset of the phenotypic characteristics acquired upon macrophage differentiation from a monocyte

Monocyte-to-macrophage differentiation with the cytokine granulocyte-macrophage colony-stimulating factor induces expression of the cyclic nucleotide phosphodiesterase PDE1B2. However, what role PDE1B2 plays in macrophage biology has not been elucidated. We have addressed this question by inhibiting PDE1B2 induction by using RNA interference. Using a retrovirus-based system, we created HL-60 stable cell lines that express a short-hairpin RNA targeting PDE1B2. HL-60 cells treated with phorbol-12-myristate-13-acetate differentiate to a macrophage-like phenotype and up-regulate PDE1B2. However, expression of PDE1B2 short hairpin RNA effectively suppresses PDE1B2 mRNA, protein, and activity up-regulation. Using the HL-60 PDE1B2 knockdown cells and agonists for either adenylyl or guanylyl cyclase, it was found that PDE1B2 predominantly regulates cGMP and plays a lesser role in cAMP regulation in response to cyclase agonists. Furthermore, in intact HL-60 cells, PDE1B2 activity can be regulated by changes in Ca+2 levels. Inhibiting PDE1B2 up-regulation does not prevent HL-60 cell differentiation, because several markers of macrophage differentiation are unaffected. However, suppression of PDE1B2 expression alters some aspects of the macrophage-like phenotype, because cell spreading, phagocytic ability, and CD11b expression are augmented. The cAMP analog 8-Bromo-cAMP reverses the changes caused by PDE1B2 knockdown. Also, PDE1B2 knockdown cells have lower basal levels of cAMP and alterations in the phosphorylation state of several probable PKA substrate proteins. Thus, the effects of PDE1B2 on differentiation may ultimately be mediated through decreased cAMP. In conclusion, PDE1B2 regulates a subset of phenotypic changes that occur upon phorbol-12-myristate-13-acetate-induced differentiation and likely also plays a role in differentiated macrophages by regulating agonist-stimulated cGMP levels.     

HIV-1 gp120 and chemokine activation of Pyk2 and mitogen-activated protein kinases in primary macrophages mediated by calcium-dependent, pertussis toxin-insensitive chemokine receptor signaling.

Human immunodeficiency virus type 1 (HIV-1) uses the chemokine receptors CCR5 and CXCR4 as coreceptors for entry. It was recently demonstrated that HIV-1 glycoprotein 120 (gp120) elevated calcium and activated several ionic signaling responses in primary human macrophages, which are important targets for HIV-1 in vivo. This study shows that chemokine receptor engagement by both CCR5-dependent (R5) and CXCR4-dependent (X4) gp120 led to rapid phosphorylation of the focal adhesion-related tyrosine kinase Pyk2 in macrophages. Pyk2 phosphorylation was also induced by macrophage inflammatory protein-1beta (MIP-1beta) and stromal cell-derived factor-1alpha, chemokine ligands for CCR5 and CXCR4. Activation was blocked by EGTA and by a potent blocker of calcium release-activated Ca++ (CRAC) channels, but was insensitive to pertussis toxin (PTX), implicating CRAC-mediated extracellular Ca++ influx but not Galpha(i) protein-dependent mechanisms. Coreceptor engagement by gp120 and chemokines also activated 2 members of the mitogen-activated protein kinase (MAPK) superfamily, c-Jun amino-terminal kinase/stress-activated protein kinase and p38 MAPK. Furthermore, gp120-stimulated macrophages secreted the chemokines monocyte chemotactic protein-1 and MIP-1beta in a manner that was dependent on MAPK activation. Thus, the gp120 signaling cascade in macrophages includes coreceptor binding, PTX-insensitive signal transduction, ionic signaling including Ca++ influx, and activation of Pyk2 and MAPK pathways, and leads to secretion of inflammatory mediators. HIV-1 Env signaling through these pathways may contribute to dysregulation of uninfected macrophage functions, new target cell recruitment, or modulation of macrophage infection.     

CCR5-binding chemokines modulate CXCL12 (SDF-1)-induced responses of progenitor B cells in human bone marrow through heterologous desensitization of the CXCR4 chemokine receptor

Although the SDF-1 (CXCL12)/CXCR4 axis is important for B-cell development, it is not yet clear to what extent CC chemokines might influence B lymphopoiesis. In the current study, we characterized CC chemokine receptor 5 (CCR5) expression and function of primary progenitor B-cell populations in human bone marrow. CCR5 was expressed on all bone marrow B cells at levels between 150 and 200 molecules per cell. Stimulation of bone marrow B cells with the CCR5-binding chemokine macrophage inflammatory protein 1beta (MIP-1beta; CCL4) did not cause chemotaxis, but CCL4 was able to trigger potent calcium mobilization responses and activation of the mitogen-activated protein kinase (MAPK) pathway in developing B cells. We also determined that CCR5-binding chemokines MIP-1alpha (CCL3), CCL4, and RANTES (CCL5), specifically by signaling through CCR5, could affect all progenitor B-cell populations through a novel mechanism involving heterologous desensitization of CXCR4. This cross-desensitization of CXCR4 was manifested by the inhibition of CXCL12-induced calcium mobilization, MAPK activation, and chemotaxis. These findings indicate that CCR5 can indeed mediate biologic responses of bone marrow B cells, even though these cell populations express low levels of CCR5 on their cell surface. Thus, by modulation of CXCR4 function, signaling through CCR5 may influence B lymphopoiesis by affecting the migration and maturation of B-cell progenitors in the bone marrow microenvironment.     

Involvement of MMP-12 and phosphodiesterase type 4 in cigarette smoke-induced inflammation in mice.

The aim of the present study was to characterise a mouse model of airways inflammation induced by cigarette smoke and to compare it with a lipopolysaccharide (LPS) model with regards to the efficacy of a PDE4 inhibitor (cilomilast), a corticosteroid (dexamethasone) and macrophage metalloelastase (MMP)-12 gene deletion. Cigarette smoke exposure for 3 days induced a time-dependent airway neutrophilia associated with an increased level of keratinocyte-derived chemokine (KC), macrophage inflammatory protein (MIP)-2, MIP-1alpha and MMP-9 in the bronchoalveolar lavage (BAL). LPS exposure also induced an increase in the number of neutrophils in BAL. Studies in MMP-12-/- mice showed that in contrast to the smoking model, MMP-12 did not have a critical role in LPS-induced inflammation. Both cilomilast and dexamethasone blocked LPS-induced neutrophilia in a dose-dependent manner. Cilomilast inhibited cigarette smoke-induced neutrophilia and MIP-1alpha, but only 10 mg.kg(-1) of dexamethasone was effective. Both anti-inflammatory treatments had no effect on the levels of KC and MIP-2 in the BAL. Although the inflammatory response was very similar in the smoking model and LPS, the pharmacological modulation and the MMP-12 gene deletion highlighted the differences in the mechanisms involved. Furthermore, the cigarette smoke model seemed to better represent the situation described in chronic obstructive pulmonary disease patients. In conclusion, these differences underline the importance of using an acute smoke-exposure model to investigate potential new treatments for chronic obstructive pulmonary disease.     

17beta-estradiol (E2) modulates cytokine and chemokine expression in human monocyte-derived dendritic cells

The effects of estrogen on the immune system are still largely unknown. We have investigated the effect of 17beta-estradiol (E(2)) on human monocyte-derived immature dendritic cells (iDCs). Short-term culture in E(2) had no effect on iDC survival or the expression of cell surface markers. However, E(2) treatment significantly increased the secretion of interleukin 6 (IL-6) in iDCs and also increased secretion of osteoprotegerin (OPG) by DCs. Furthermore, E(2) significantly increased secretion of the inflammatory chemokines IL-8 and monocyte chemoattractant protein 1 (MCP-1) by iDCs, but not the production of the constitutive chemokines thymus and activation-regulated chemokine (TARC) and macrophage-derived chemokine (MDC). However, after E(2) pretreatment the lipopolysaccharide (LPS)-induced production of MCP-1, TARC, and MDC by DCs was clearly enhanced. Moreover, mature DCs pretreated with E(2) stimulated T cells better than control cells. Finally, we found that E(2) provides an essential signal for migration of mature DCs toward CCL19/macrophage inflammatory protein 3beta (MIP3beta). In summary, E(2) may affect DC regulation of T-cell and B-cell responses, as well as help to sustain inflammatory responses. This may explain, in part, the reason serum levels of estrogen correlate with the severity of certain autoimmune diseases.     

Nasal cytokine and chemokine responses in experimental influenza A virus infection: results of a placebo-controlled trial of intravenous zanamivir treatment.

The local immune response to influenza virus infection was characterized by determining cytokine and chemokine levels in serial nasal lavage fluid samples from 15 volunteers experimentally infected with influenza A/Texas/36/91 (H1N1). The study was part of a randomized double-blind placebo-controlled trial to determine the prophylactic effect of intravenous zanamivir (600 mg 2x/day for 5 days), a highly selective inhibitor of influenza A and B virus neuraminidases, on the clinical symptoms of influenza infection. Nasal lavage fluid levels of interleukin (IL)-6, tumor necrosis factor-alpha, interferon-gamma, IL-10, monocyte chemotactic protein-1, and macrophage inflammatory protein-1alpha and -1beta increased in response to influenza virus infection and correlated statistically with the magnitude and time course of the symptoms. Treatment with zanamivir prevented the infection and abrogated the local cytokine and chemokine responses. These results reveal a complex interplay of cytokines and chemokines in the development of symptoms and resolution of influenza.     

Interleukin-1beta induces phosphodiesterase 4B2 expression in human myometrial cells through a prostaglandin E2- and cyclic adenosine 3',5'-monophosphate-dependent pathway

Intrauterine infections are important etiological factors of preterm labor. They trigger an increase in proinflammatory cytokines, in particular IL-1beta, that induces a cascade of events resulting in the production of potent effectors of myometrial contractility, such as the prostaglandin E(2) (PGE(2)). Within the smooth muscle cells, contractility is under the control of cAMP content, partly regulated by cAMP-phosphodiesterase 4 (PDE4), the predominant family of PDEs expressed in human myometrium. In the present study, using a model of inflammation of human myometrial cells in culture, we demonstrated that exposing the cells to IL-1beta resulted in a significant up-regulation of PDE4 activity through an increase in PDE4B2 mRNA and protein levels. The IL-1beta-induced PDE4 activity occurs after an increase in PGE(2) production and subsequent cAMP augmentation. Pretreatment with indomethacin or NS 398 completely blocked this long-term effect of IL-1beta, revealing a PGE(2)-dependent pathway. Accordingly, our results demonstrated that the PDE4B2 variant can participate in the regulation of the inflammatory reaction that occurs at term or in preterm labor and leads to myometrial contractions. Knowing the myorelaxant effect of PDE4 inhibitors and the implication of the PDE4B2 in the inflammatory process, this isoform may be an appropriate target for discovering antiinflammatory drugs to manage infection-induced preterm deliveries.     

Dichotomy in duration and severity of acute inflammatory responses in humans arising from differentially expressed proresolution pathways

Lipoxins (Lxs) and aspirin-triggered epi-Lxs (15-epi-LxA₄) act through the ALX/FPRL1 receptor to block leukocyte trafficking, dampen cytokine/chemokine synthesis, and enhance phagocytic clearance of apoptotic leukocytes—key requisites for inflammatory resolution. Although studies using primarily inbred rodents have highlighted resolution as an active event, little is known about the role resolution pathways play in controlling the duration/profile of inflammatory responses in humans. To examine this, we found two types of responders to cantharidin-induced skin blisters in male healthy volunteers: those with immediate leukocyte accumulation and cytokine/chemokine synthesis followed by early resolution and a second group whose inflammation increased gradually over time followed by delayed resolution. In early resolvers, blister 15-epi-LxA₄ and leukocyte ALX were low, but increased as inflammation abated. In contrast, in delayed resolvers, 15-epi-LxA₄ and ALX were high early in the response but waned as inflammation progressed. Elevating 15-epi-LxA₄ in early resolvers using aspirin increased blister leukocyte ALX but reduced cytokines/chemokines as well as polymorphonuclear leukocyte and macrophage numbers. These findings show that two phenotypes exist in humans with respect to inflammation severity/longevity controlled by proresolution mediators, namely 15-epi-LxA₄. These data have implications for understanding the etiology of chronic inflammation and future directions in antiinflammatory therapy.